1. FIELD OF THE INVENTION
This invention relates to the measurement of the gas content of a closed or sealed container after degassing by a special valving technique, a gas specific probe or probes, and microprocessor based software.
2. DESCRIPTION OF THE BACKGROUND
AIR CONTENT
Air content--via the oxygen component of air--in a liquid is a quantity that is of interest to the canning industry in general and the beverage industry in particular. The current generally accepted method for measuring the air content in a beverage liquid (usually carbonated) is by a non-electronic chemical technique. The conventional method for measuring the air content in a carbonated beverage is a chemical test using a hydroxide solution. The hydroxide solution is used to absorb CO.sub.2 and while a 10% solution will work, a stronger solution will function more rapidly and is less quickly diluted by beer which works up the Burrette. After the test is finished, the valve assembly should be thoroughly flushed with water to remove the sample (Zahm Practical Testing Instruments 15th Edition, pages 12 and 13).
Although it might be theoretically possible to make a measurement in the liquid, such a measurement is both difficult mechanically and difficult to analyze. The interpretation of the data because of solubility problems which are a function of additives (wanted and unwanted) would be very complex and troublesome. Temperature and pressure variations are also a problem. Air is primarily nitrogen and oxygen in approximately a 4 to 1 ratio (80% nitrogen, 20% oxygen). There is no direct electronic measurement for nitrogen but air content can be calculated by measuring the oxygen component. Also this measurement can separate the amount of air in the head space of a drink (that space that is not occupied by liquid) from the air in the beverage.
SPECIAL PROBLEMS (SPEED OF TEST AND INTERFERENCES)
The method of measuring a gas in summation, that is, a little at a time with a running total, in some cases is too slow. The reasons vary and are:
(i) too much pressure build up from a competing gas, PA1 (ii) interference at the sensor by a competing gas, PA1 (iii) slow distribution of the gas in the measure chamber. PA1 (i) The polarographic probe measures oxygen through a physical chemical process that converts oxygen to an electronic signal. The general equations are: At the gold cathode: ##STR1## (ii) Ultrasonics is a conventional and convenient method of degassing a liquid. Air is less soluble than CO.sub.2. The overwhelming amount of CO.sub.2 in the liquid pushes the small amount of air out of the liquid and the head space and eventually into a test chamber above. PA1 (iii) A microprocessor device provides control of the calibration and measuring sequences.
POLAROGRAPHIC SENSORS
A direct comparison can be made; that is, the ratio of air in the test mode to air in the calibration mode is the same as the ratio of oxygen in the test mode to oxygen in the calibration mode. ##EQU1## In a carbonated beverage there are primarily two forms of gas present. The desired gas is CO.sub.2 and the undesirable gas is air. (A description of CO.sub.2 measurement can be found in U.S. Pat. No. 4,607,342 which is hereby specifically incorporated by reference--Apparatus for Remotely Measuring and Controlling the Carbon Dioxide in a Beverage Liquid: On-Line). This invention measures the air content in the beverage which is ideally zero. There are several technologies employed to accomplish this measurement.
SPECIFIC SPECTRAL SENSORS
The specific CO.sub.2 sensor is characterized by a self-calibrating device as described by Wong (U.S. Pat. No. 4,578,762 which is hereby specifically incorporated by reference). This device has been reduced in size and now is suitable for inclusion in a system that measures the CO.sub.2 component in beverage gases, and environmental gases such as the CO.sub.2 consumed by bacteria. Another type of oxygen device for measuring O.sub.2 released by bacteria is a specific spectral device in the visible red (Wong U.S. Pat. No. 4,730,112 which is hereby specifically incorporated by reference). This has also been reduced in size so that it is suitable for instrumentation.
APPLICATIONS TO ENVIRONMENTAL FIELDS
These techniques can also be applied to some environment problems such as BOD (Biological Oxygen Demand) and bacteria nourishment in composting. In BOD measurements, the liquid sample of interest can be contained in a batching chamber and the oxygen gas (or specific gas component) can be removed by bubbling techniques. In composting, the compost heap can be considered a source of oxygen and CO.sub.2 along with other gases.
BOD DEMAND
In certain circumstances, the quality of water is determined by its oxygen content. Most often the probes are placed directly in the liquid. However, by bubbling an inert gas through the liquid we will be able to remove oxygen to determine the biological oxygen demand and chemical oxygen demand. This is a direct outgrowth of the methodology for removing oxygen from a sealed container with no CO.sub.2 or internal purge gas. The sealed container in this gas is a fixed volume of liquid that is contained in a "batching chamber" that has entrance and exit valves. When these valves are closed, the "batching chamber becomes a sealed container. An example of a batching chamber is described in Selden (U.S. Pat. No. 4,607,342 which is hereby specifically incorporated by reference).
COMPOSTING
A composting technique is at the center of many attempts to clean up the environment. The main gases that concern bacteria are CO.sub.2 and O.sub.2, and these gases to a large measure determine the activity of the bacteria which in turn determines how effectively they are eliminating (digesting) the pollutant of interest (gasoline, hydrocarbons, toxins, harmful metals, poisons, and pesticides). Normally the gas is measured flowing in a pipe.
BACKGROUND FOR DETERMINING BINARY MIXTURES IN A BEVERAGE GAS--PRINCIPALLY N.sub.2 AND CO.sub.2
The second major component in air is nitrogen. There is no specific spectral or polarographic method for measuring nitrogen gas. In certain beverages, a large amount of N.sub.2 is added. If the system is basically a binary system, that is large amounts of CO.sub.2 and N.sub.2, then a double test will isolate the two gases. The two tests would be the non-specific pressure temperature test, sometimes referred to as the Heath test and a more specific CO.sub.2 test. In some cases alternative degassing techniques must be used. In many cases an external gas will be bubbled through the liquid in the test container to expel the specific gas of interest.
The brewing industry in England adds nitrogen gas to their product for several reasons; one being that it "improves the quality of the head". Also low carbonation drinks need extra pressure internally in cans so that they will not collapse when piled on each other.
Since this device, as it is, analyzes two gases CO.sub.2 (non-specific) and O.sub.2 (trace gas-specific), it is desirable to add an N.sub.2 measurement to our instrument, because the non-specific CO.sub.2 measurement is useless if large amounts of nitrogen are added. In many cases N.sub.2 is added to the beverage so in that situation the N.sub.2 content of the drink would have no relationship to the O.sub.2 content (in air 4 to 1). The pressure-temperature (Heath) measurement is only valid in a one component system (CO.sub.2). To analyze the two major gases (CO.sub.2 and N.sub.2 --binary mixture), some existing technologies have been explored including molecular sieve, membrane, and several versions of thermal conductivity. These techniques all attempt to measure N.sub.2 as such.
One method allows the gas to pass over a resistive element to measure the CO.sub.2 /N.sub.2 mixture relative to 100% CO.sub.2. The gas would be removed from the head space after agitation. The pressure-temperature (Heath) method will give us a total gas number, while the resistive element will give a relative number allowing us to determine the percent concentration for the binary system (CO.sub.2 and N.sub.2).
Another method for uniquely determining one of the two components in the binary mixture involves the well established technique of infrared absorption using one of the spectral lines of CO.sub.2 (probably 4.3 microns). Neither N.sub.2 nor O.sub.2 have an infrared spectrum due to their symmetry (O.sub.2 does have a slight spectrum in the far red near 0.79 microns).
Either one of these methods (or both)--thermal conductivity; CO.sub.2 absorption--coupled with the additional information derived from the Heath (pressure/temperature) measurement (and additional mathematics) will allow the determination of each of the two components. The difference is that one method--thermal conductivity--is a non-spectral technique; which the second CO.sub.2 absorption--is a specific spectral technique and is very precise. Basically, two equations in two unknowns are solved.
In summary, gases other than CO.sub.2 and O.sub.2 may be present in certain beverages. Usually this gas is nitrogen (N.sub.2). Since our device measures CO.sub.2 non-specifically (see U.S. Pat. No. 4,607,342 which is hereby specifically incorporated by reference) and O.sub.2 (trace) specifically, we cannot separate CO.sub.2 from N.sub.2 (binary mixture) without another measurement. Also tertiary or greater mixtures of gases can be analyzed. Molecular sieves, membranes, and resistive techniques have been used for such separations. CO.sub.2 absorption is another technique.